Single-pass pallet disassembler with self-adjusting head

ABSTRACT

An apparatus for unnailing wood pallets includes a frame, a first cutter assembly and a second cutter assembly positioned vertically above the first. The first cutter assembly includes a pair of elongated horizontal support arms supporting a cutting head at one end, downwardly biasing springs at an opposite end and a pivot between the ends. The second cutter assembly includes a pair of elongated horizontal support arms supporting a second cutting head at one end and a pivot at an opposite end that is coaxial the pivot of the first cutter assembly. The second cutter assembly is biased upwardly by springs between its support arms and those of the first cutter assembly. A stringer return member is horizontally movable with a pallet-moving cradle and includes a member which is pivotally mounted to the cradle at one end and has a follower at an opposite end to follow a track that moves with the support arms in order to keep the member positioned between the pair of support arms. Each cutting head includes a pair of circular cutting blades having an outer portion that is hardened and a center portion that is left ductile. A sacrificial backing block on the pallet-moving cradle forces the pallet against the blades so that if any contact is made between the cradle and the blades, the sacrificial member, not the blades, will be damaged.

BACKGROUND OF THE INVENTION

This invention relates to an apparatus for disassembling a woodenarticle and is especially adapted for disassembling wooden pallets inorder to replace broken boards. More particularly, the inventionconcerns an apparatus that is capable of breaking the nails between theslats and a supporting stringer on both sides of the stringer during asingle pass through the apparatus.

U.S. Pat. No. 3,869,780 to Ginnow et al for an UNNAILER discloses apractical apparatus for disassembling wooden pallets and includes a pairof free-rotating circular blades carried by an elongated support armmounted at one end of a frame. A pallet is moved relative to thecircular blades to effect cutting of the nails by the relative movementbetween the pallet and the blades. The support arms are side-by-sidehorizontal cantilevered arms. The complicated, failure-prone means foraligning the interface between the pallet slats and stringer in theGinnow et al patent was replaced in subsequent designs by self-aligningmeans for aligning the cutting blades with the interface.

Because the Ginnow et al apparatus cuts the nails on one side of astringer, six passes were required to completely disassemble a pallet.In Williams U.S. Pat. No. 4,320,570 and 4,435,892 for an apparatus andmethod of disassembling wooden pallets, three sets of side-by-sidesupport arms and rotary cutting blades are positioned to simultaneouslycut the nails on one side of three pallet stringers such that only twopasses are required to disassemble a pallet. The Williams method andapparatus has met with limited success because of the complexityinvolved including the necessity for providing lateral adjustability tothe support arms.

Other techniques, that deviate from the general approach suggested inthe Ginnow et al patent, have been suggested in the prior art. Forexample, U.S. Pat. No. 4,241,495 issued to Wakeem for a METHOD ANDAPPARATUS FOR DISASSEMBLING WOODEN PALLETS, discloses three pair ofmotor-driven rotary cutters that are vertically applied to an on-endpallet. Each set of cutters includes positioning fingers for contactingthe inner surface of the slats to guide the driven cutters into thespace between the slats in the stringer. This patent not only requireslateral adjustment of the cutting heads to match the stringers, butprovides motor-driven cutters with adjustable-length drive shafts toaccommodate various stringer widths. Such complexities, which increasedown-time, thwart the very goal of the design, which is to increaseproductivity.

In addition to difficulties in achieving increased productivity, otherdeficiencies in the basic Ginnow device remain. The cutting blades,which are an expensive item and require substantial machine down-time toreplace, are prone to a catastrophic failure mode in which the severestress of cutting hardened nails causes the blade to sever laterallyinto two or more pieces. In addition, the necessity of moving a palletsufficiently forward across the blades in order to sever the nails foreach slat, requires that a portion of the pallet-moving mechanism comeperilously close to the blades, resulting in occasional metal-to-metalcontact, which further damages the blades. Thus, the need exists for apallet disassembler which provides enhanced productivity while improvingreliability and durability.

SUMMARY OF THE INVENTION

The need for enhanced productivity and reliability in disassemblingwooden pallets is met in an apparatus including first and second cuttingmeans for cutting nails and means for causing relative horizontalmovement between a wooden pallet and the first and second cutting means.A first support means is provided for supporting the first cutting meansand a second support means is provided for supporting the second cuttingmeans vertically above the first cutting means. Self-aligning guidemeans on each of the first and second support means guide the associatedcutting means through the interface between a pallet stringer and oneset of slats. An apparatus according to this aspect of the invention,severs the nails from both sides of a stringer simultaneously, reducingto three the number of passes to disassemble an entire pallet.Preferably, the first support means includes a first horizontal memberwith the first cutting means at one end and including means for biasingthe opposite end downwardly. The first horizontal member is pivotablymounted to a frame at a location between the ends. The second supportmeans includes an elongated second horizontal member having oppositefirst and second ends. The second cutting means is positioned at thefirst end and means are provided for pivotally mounting the member tothe frame at an opposite end. Means are provided for biasing the firstend upwardly.

One difficulty that is overcome, according to another aspect of theinvention, is that of returning the stringer board along with theremaining portions of the pallet after passing the stringer between thefirst and second cutting means. Because of the self-aligning actionprovided by the guide means, any stationary member on the pallet movingmeans adapted to returning the stringer would be unworkable because itwould jam the stringers and often contact the cutting means. Thus,according to this aspect of the invention, means are provided forreturning the stringer with the rest of the pallet remains, includingmeans that are movable with at least one of the supports for the cuttingmeans that defines a track. A stringer return member having a surfacefor abutting a stringer and a follower for following the track ismounted to the pallet moving means such that the member horizontallymoves with the pallet moving means and the follower is verticallyadjustable in order to allow it to follow the track. In this manner, thestringer return member retains its position between the supports for thefirst and second cutting means while horizontally moving with the palletmoving means.

According to yet another aspect of the invention, catastrophic failureof rotary cutting blades in such a pallet disassembly apparatus issignificantly reduced by providing cutting blades in which a hardeningprocess is applied to the portion of the blade immediately adjacent thecutting edge while the central portion is left substantially unhardened.In this manner, the blade is able to absorb the stresses imparted by theunnailing process rather than catastrophically failing.

In yet another aspect of the present invention, blade damage issignificantly reduced by providing a sacrificial member, which is itselfnondamaging to the blades, at the portion of the pallet moving meansthat comes closest to the blades. Thus, when this portion of the palletmoving means does come into contact with the blades, only thesacrificial member will be damaged. The sacrificial member is relativelyinexpensive and easy to replace and, therefore, provides a greatadvantage.

These and other related objects, advantages and features of thisinvention will become apparent upon review of the followingspecification in conjunction with the drawings.

DRAWINGS

FIG. 1 is a side elevation of an apparatus embodying the invention;

FIG. 2 is a top plan view of the apparatus in FIG. 1;

FIG. 3 is a sectional view taken along the lines III--III in FIG. 2;

FIG. 4 is a partial side elevation taken along the lines IV--IV in FIG.2;

FIG. 5 is a partial plan view taken along the lines V--V in FIG. 4;

FIG. 6 is a partial end elevation taken along the lines VI--VI in FIG.5;

FIG. 7 is a sectional view taken along the lines VII--VII in FIG. 2;

FIG. 8 is a sectional view taken along the lines VII--VII in FIG. 2;

FIG. 9 is a bottom plan view of the lower cutting head assembly;

FIG. 10 is a top plan view of the upper cutting head portion;

FIG. 11 is a partial side elevation of a stringer return assemblyembodying the present invention;

FIG. 12 is an end elevation taken from the direction XII in FIG. 11;

FIG. 13 is a bottom plan view taken along the lines XIII--XIII in FIG.11;

FIG. 14 is a side elevation of a pallet cradle including a sacrificialbackup block embodying the present invention;

FIG. 15 is a sectioned elevation of a blade assembly embodying thepresent invention; and

FIG. 16 is a bottom plan view taken along the lines XVI--XVI in FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now specifically to the drawings, and the illustrativeembodiments depicted therein, a pallet disassembler 20 includes a frame22, an elongated cutting head assembly 24 and pallet moving meansincluding a pallet support cradle 26 and propulsion means, such as ahydraulic cylinder 28 (FIGS. 1 and 2). Cutting head assembly 24 includesan upper arm assembly 30 and a lower arm assembly 32, both of which are,in the illustrated embodiment, pivotally mounted to frame 22 about acommon pivot axis 34. The space under head 24 forward of pivot axis 34(to the left, as viewed in FIG. 1) is unobstructed such that palletsupport cradle 26 is movable from a first, retracted positionillustrated in FIG. 1 to a second, extended position under head assembly24 by the extension of hydraulic cylinder 28. Cradle 26 is guided inthis movement by lateral wheels (not shown) operating in guides (notshown) formed in the sides of frame 22. Pallet disassembler 20 furtherincludes a hydraulic oil reservoir 36 and appropriate hydraulic controls37.

Lower arm assembly 32 includes an elongated support member, generallyillustrated as 38, and cutting means 40 positioned at end portion 42 ofthe support member (FIG. 9). Support member 38 is made from mirror-imagesupport arms 44a and 44b, which are rigidly interconnected at endportion 42 by a bridge plate 46 and at an opposite end portion 50 by asecond bridge plate 48. Chamfered nose portions 52a, 52b, which extendforwardly at end portion 42, provide means for aligning the cuttingmeans 40 with the interface between a stringer 100 and a set of slats ona pallet, as will be set forth in more detail below and as illustratedin FIG. 3. Cutting means 40 includes a pair of free-rotating cuttingblade assemblies 54a, 54b whose circular cutting edges slightly overlap.Adjustability of blade assemblies 54a, 54b is provided by lateraladjustment means 56a, 56b. Elongated guide rails 58a, 58b are welded toa lower surface of support arms 44a, 44b for a purpose that will be setforth in more detail below. An upward bias is imparted to the cuttingend portion 42 of lower arm assembly 32 by downwardly extending biasingmeans 58 which bias end portion 50 toward frame 22 (FIG. 1). In theillustrated embodiment, biasing means 58 includes a pair of compressionsprings 60, each having an 800 pound rating, and adjustable mountingmeans, including a nut 62, threadably engaging bolt 64 extending fromportion 50. The bias is preferably adjusted to provide a 30 pound netdownward bias to end portion 42.

By reference to the FIG. 10, upper arm assembly 30 includes elongatedupper support member 66 and upper cutting means 68 positioned at endportion 69 of the support member. Support member 66 includes a pair ofmirror-image support arms 70a, 70b rigidly interconnected by forwardbridge plate 72 and rearward bridge plates 74a, 74b. Pivot 34 is locatedat an end portion 76 of upper arm assembly 30 that is opposite thecutting end portion 69. A pair of guide rails 78a, 78b are welded to anupper surface of support arms 70a, 70b and cooperate with guide rails58a, 58b in a manner that will be set forth below. Cutting means 68 areidentical with cutting means 40 on the lower arm assembly and includefree-rotating cutting blade assemblies 80a, 80b. Upper arm assembly 32additionally includes nose portions 82a, 82b defined by a chamfered,tapered portion of support arms 70a, 70b.

The structural relationship between upper arm assembly 30 and lower armassembly 32 may be better understood by reference to FIGS. 7 and 8, inwhich it may be seen that each support arm 44a, 44b, 70a, 70b is achannel member. Upper support arms 70a, 70b are inverted and laterallyoffset from lower arms 44a, 44b such that the upper and lower arms maynest together and pivot about common pivot axis 34. The pivot means at34 includes a steel shaft 84 supported by blocks 86a, 86b, 86c andbushings 87 welded to lateral sides of each support arm. An upward biasis provided to the cutting end portion 69 of upper arm assembly 30 byhead springs 88a, 88b positioned between the support arms 44a and 70a,and head springs 88c, 88d positioned between support arms 44b and 70b.The head springs 88a-88d are positioned at end portion 69, which is theend of the cutting head assembly that is opposite the pivot. Thus, agreater upward force may be provided to cutting end portion 69 bysmaller springs. In addition, the location of the head springs 88a-88dbetween the upper and lower support arms provides shielding from damagecaused by the pallet disassembly process. Restraining bolts 90a, 90bwelded to upper support arms 70a, 70b and extending through openings inlower support arms 44a, 44b, threadably receive adjustment nuts 92a, 92bin order to provide constraint on the amount of upward travel of theupper support arms 70a, 70b with respect to the lower supports arms 44a,44b. Adjustment nut 92 provides for adjustment of the travel limit and,when removed, additionally allows separation of the support arms toprovide access to head springs 88a-88d. In a preferred embodiment, headsprings 88a-88d are preselected to provide a net 30 pound upward bias tocutting end portion 69 of upper arm assembly 30.

Nose portions 52a, 52b include downward, rearwardly sloping surfaces94a, 94b and end nose portions 82a, 82b include upward, rearwardlysloping surfaces 96a, 96b (FIG. 4). Blade assemblies 54a, 54b includesubstantially planar lower surfaces 98a, 98b that are aligned with thetrailing edges of sloping surfaces 94a, 94b. Likewise, upper cuttingblade assemblies 80a, 80b include substantially planar upper surfaces99a, 99b that are aligned with the trailing edges of sloping surface96a, 96b. In this manner, nose portions 52a; 52b guide the cutting edgesof cutting blade assemblies 54a, 54b to the interface between a stringer100 and the bottom slats (not shown) and nose portions 82a, 82b guidecutting assemblies 80a, 80b to the interface between stringer 100 andthe upper slats of the pallet (not shown).

Bridge plates 46, 72 include chamfered leading edges 102, 104 anddouble-beveled trailing edges 106, 108, respectively (FIG. 4). Thepurpose of leading chamfered edges 102, 104 is to guide the denailedslats away from the stringer as the pallet is progressively moved alongcutting head assembly 24. The purpose of double beveled trailing edges106 and 108 is important to the return stroke during which the denailedstringer, which is now separate from the pallet, is being returned tothe initial position of the cradle illustrated in FIG. 1, along with theremaining portions of the pallet. It has been discovered that, if thetrailing surface of bridge plates 46, 72 are chamfered in the samemanner as the leading surface 102, 104, certain difficulties arise. Acommon form of pallet includes notched surfaces on the stringers inorder to allow a forklift to approach the pallet from all four sides.When such a pallet is disassembled and such a notch approaches thebridge plate during the return stroke, there is a tendency for thestringer to offset in the direction of the notch. The double-beveledtrailing surfaces 106, 108 guide the stringer back into the spacebetween the support arms to prevent the notches in the stringers fromjamming the bridge plates and shutting down the apparatus.

Pallet support cradle 26 includes a bed plate 110 and forward and rearplates 112, 114, respectively. During the forward stroke, rear plate 114exerts a forward thrust on the pallet against cutting head assembly 24.Upon completion of the forward stroke, front plate 112 returns most ofthe disassembled pieces of the pallet to the position illustrated inFIG. 1. However, front and rear plates 112, 114 must be open in thecenter in order to allow the cutting head to traverse the front and rearplates. During the return stroke of the pallet cradle 26, this openingin front plate 112 prevents the front plate from returning the stringerto the position illustrated in FIG. 1. In order to return the stringerwith the remaining portions of the disassembled pallet, a stringerreturn means 116 is provided.

By reference to FIGS. 7 and 11-13, stringer return means 116 includes avertical support 118 which is attached at its lower end to center beammembers 120a, 120b of cradle 26. Center beam members 120a, 120b providea point for attachment of support deck 110 and hydraulic cylinder 28 tothe cradle. A stringer return arm 122 is pivotally mounted at 124 to anupper portion of support 118 by means such as a shear-pin. Stringerreturn arm 122 includes a forward-facing surface 126 at an opposite endfrom support 118 and laterally extending side portions 128a, 128badjacent surface 126. Side portions 128a, 128b are configured forpositioning within a space 129 defined between guide rail members 57a,57b and 78a, 78b (FIG. 7). Because stringer return arm 122 is pivotablymounted to support 118, side portions 128a, 128b are followers whichfollow the relative movement of upper and lower arm assemblies 30, 32and thus position forward-facing surface 126 between the arm assemblies.Stringer return arm 112 is made from ultra-high molecular weight polymer(UMWP) which is selected because of its self-lubricating properties.This material is also preferred because stringer return arm 122 will bepassing repeatedly between the cutting blade assemblies, any inadvertentcontact between the arm and the cutting blades will typically causeminor damage to the stringer return arm but no damage to the bladeassemblies. Even an occasional failure of the stringer return arm can bereadily fixed at a relatively low cost.

By reference to FIG. 14, pallet cradle 26 additionally includes a backupblock 130 which extends forwardly through an opening 132 in rear plate114. Backup block 130 is positioned within opening 132 by a bracketassembly 134 extending upwardly from under bed 110 of the cradle. Backupblock 130 is a sacrificial member made from a material preselected to bedamaged by, rather than cause damage to, the blade assemblies. As cradle26 is thrust fully forward in order to sever the rearmost slat of thepallet, a portion of the cradle must be thrust very close to the bladeassemblies. Backup block 130 is positioned at the portion of the cradlethat comes closest to the blade assemblies so that if any part contactsthe blades, it will be the backup block. In the illustrated embodiment,backup block 130 is made from UMWP and is attached to cradle assembly 26in a manner to be easily replaceable.

Each blade assembly 54a, 54b, 80a, 80b includes a circular cutting blade136 and free-rotating mounting means, generally illustrated as 138, formounting the cutting blade to the respective support arm (FIGS. 3, 15and 16). Each cutting blade 136 includes an inner portion 140 includinga central hole 142 extending through the blade. A plurality ofcountersunk fastener openings 148 are distributed around hole 140. Eachcutting blade 136 additionally includes an outer portion 144 whichdefines a cutting edge 146. Mounting means 138 includes a spindle 150having an enlarged portion 152 dimensioned to provide an interferencefit with an opening in the respective support arm. Spindle 150additionally includes a narrow portion 154 which is dimensioned toprovide an interference fit with the inner race 156 of a bearing 158. Anouter race 160 of bearing 158 is captured between a flange 162 definedaround opening 142 and a retainer 164. Thus, with spindle portion 152press-fit into its corresponding support arm, with spindle portion 154press-fit into inner race 156 and with fasteners (not shown) extendingthrough countersunk openings 148 in blade 136 and extending intoopenings 166 in retainer 164, blade 136 is firmly rotatably mounted toits corresponding support arm. As best seen by reference to FIGS. 3 and4, cutting assemblies 54a, 54b, 80a, 80b are mounted with a slight cantlaterally and forwardly of 2.5°.

A retainer cap 168 includes an inwardly extending outer groove forreceiving an O-ring 170 or other like sealing means. With fasteners (notshown) extending through openings 172 in retainer cap 168 and receivedin openings 174 in spindle 150, retainer cap 168 is positioned within anarrow portion 176 of hole 142. With O-ring 170 sealing the interfacebetween blade 136 and retainer cap 168, the retainer cap will serve toretain grease in the space surrounding the races of bearing 158 whileminimizing the amount of wood particles entering the bearing which maycause damage thereto. Thus, while not completely eliminating damage tobearings 158, the illustrated mounting means substantially extends thelife expectancy of such bearings.

Cutting blade 136 is not uniformly hardened as is conventional in thepallet disassembly art. Rather, only outer portion 144 is hardened andinner portion 140 is left unhardened and is, therefore, ductile. It hasbeen discovered that this arrangement significantly reduces the tendencyof such cutting blades to experience catastrophic failure that occurs inprior blades that are hardened throughout. In fact, while a slightreduction in the useful life of a ground edge 146 is experienced, noblade made in this fashion has yet experienced a catastrophic failureduring a trial period that would have produced several such failures inthe prior fully-hardened blades. Because the edge 146 may be readilyrestored by grinding, the significant reduction in catastrophic failuresis a vast improvement. In the illustrated embodiment, blade 136 is madefrom 4140 steel that is flame-hardened for approximately one inch of itsouter perimeter to a 58-60 Rockwell hardness.

In operation, with a pallet placed on cradle 26 and a stringer 100generally laterally aligned with cutting head 24, hydraulic controls 37are actuated to cause cylinder 28 to fully extend. As contact is madebetween the pallet and the cutting head, nose portions 52a, 52b, 82a,82b cause the upper and lower arm assemblies to vertically adjust andalign the cutting plane of blade assemblies 54a, 54b, 80a, 80b with theinterface between stringer 100 and the upper and lower slats. In theillustrated embodiment, sufficient self-aligning capability is providedto accommodate stringers from 3-41/2" in height and slats from 1/2 to11/2" in thickness. As the pallet passes over the cutting blades, theleading edges 102, 104 of bridge plates 46, 72 cause the slats to expandaway from the stringer. When the cylinder 28 is fully extended, backupblock 130 will extend in the area adjacent the cutting blades and thrustthe pallet fully beyond the cutting blades. When the operator actuatescontrols to withdraw cradle 26, front surface 126 of stringer return arm122 will retrieve the stringer from the area 129 between the supportarms under the horizontal thrust provided by support 118 through pivot124. Side portions 128a will guide stringer return arm 122 forwardlybetween the cutting blade assemblies to avoid jamming and damage. As thestringer engages bridge plates 46 and 72, double bevel trailing edges106 and 108 guide the stringer towards the area between the support armsto avoid jamming. By returning the stringer along with the remainingportions of the disassembled or partially-disassembled pallet, anoperator standing at one end of the apparatus may load the apparatuswith pallets and remove all of the pallet components with little motion.

Because the nails on both sides of a stringer are simultaneously cut ina single pass through the disassembler 48, an entire pallet may bedisassembled with three passes versus the traditional six passesrequired by conventional pallet disassemblers. In addition, the presentinvention avoids the complicated mechanisms provided by prior attemptsto enhance productivity and, further, eliminates many of thefailure-prone structures of even relatively simple prior art machines.Furthermore, the present apparatus is less prone to jamming and, whensuch jamming does occur, the apparatus is configured to avoid damage tocritical components.

The present invention provides self-alignment with both the upper andlower slats through a pivotal motion which provides durability. Bypivoting upper and lower arm assemblies about a common pivot that isspaced a large distance from the cutting blades, the vertical movementof the cutting blades, as they self-align, does not result insubstantial angular displacement of the cutting blade axis and thuseliminates a source of board gouging.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the principles of the inventionwhich is intended to be limited only by the scope of the appendedclaims, as interpreted according to the principles of patent lawincluding the doctrine of equivalents.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows.
 1. An apparatus forunnailing wood pallets having first and second spaced sets of slatsnailed to opposite sides of a plurality of wood stringers, saidapparatus comprising:a frame; a first arm assembly including anelongated horizontal first member having opposite first and second endportions and first cutting means at said first end portion thereof forcutting nails, said first arm assembly further including pivot means forpivotally mounting a portion of said first member between said oppositeend portions to an end of said frame to pivot about a horizontal axisand biasing means for biasing said second end portion thereofdownwardly; a second arm assembly including an elongated horizontalsecond member having opposite first and second end portions and secondcutting means at said first end portion thereof for cutting nails, saidsecond cutting means positioned vertically above said first cuttingmeans, said second arm assembly further including second pivot means forpivotally mounting said second end portion of said second member to saidend of said frame to pivot about a horizontal axis and biasing means forbiasing said first end portion thereof upwardly; guide means on saidfirst end portions of said first and second members for guiding saidfirst and second cutting means to opposite interfaces between a palletstringer and the first and second associated sets of slats; and palletmoving means mounted to said frame for moving a pallet horizontally inthe direction of said first and second arm assemblies.
 2. The apparatusin claim 1 in which said first and second pivot means are positioned tomount said first and second members to pivot about a common axis.
 3. Theapparatus in claim 1 in which said first biasing means includes atension spring extending between said second end portion of said firstmember and said frame.
 4. The apparatus in claim 1 in which said secondbiasing means includes a compression spring extending between said firstend portions of said first and second members.
 5. The apparatus in claim4 further including means for limiting the separation of said first endportions
 6. The apparatus in claim 1 in which said guide means includesan outwardly downwardly sloping surface on said first member and anoutwardly upwardly sloping surface on said second member.
 7. Theapparatus in claim 1 further including stringer return means positionedbetween said first and second members and attached to said palletsupport means for moving a stringer in a direction away from said firstand second members.
 8. An apparatus for unnailing wood pallets havingfirst and second spaced sets of slats nailed to opposite sides of aplurality of wood stringers, said apparatus comprising:a frame; a lowerarm assembly including a pair of generally horizontal laterally spacedelongated first arms, first connecting means for rigidly interconnectingsaid first arms, first circular blades positioned horizontally on oneend of said first arms in a manner that said blades overlap in ashearing fashion, first biasing means for biasing downwardly an end ofsaid first arms opposite said first ends, pivot means between said endsof said first arms for mounting said lower arm assembly to said frame topivot about a horizontal axis, and guide means at said first ends ofsaid first arms for guiding said first circular blades to an interfacebetween a stringer and a set of slats; an upper arm assembly above saidlower arm assembly and including a pair of generally horizontallaterally spaced elongated second arms, second connecting means forrigidly interconnecting said second arms, second circular bladespositioned horizontally on one end of said second arms above said firstcircular blades, second pivot means at an end of said second armsopposite said first ends thereof for mounting said upper arm assembly topivot about said axis, biasing means between each of said first arms andthe juxtaposed one of said second arms for biasing said first ends ofsaid arms apart, and guide means at said first ends of said second armsfor guiding said second circular blades to an interface between astringer and a set of slats; a pallet support cradle horizontallymovable on said frame between a first position away from said armassemblies and a second position under said arm assemblies, said supportcradle including a horizontal surface and opposite end surfacesgenerally perpendicular to said first and second arms; and means formoving said pallet support cradle between said first and secondpositions.
 9. The apparatus in claim 8 further including means forlimiting the separation of said upper and lower arm assemblies.
 10. Theapparatus in claim 8 further including stringer return means for movinga stringer from said second position to said first position, saidstringer return means including track means defining a track betweensaid upper and lower arm assemblies and a ram member horizontallymovable with said pallet support cradle and including a portion guidedalong said track.
 11. The apparatus in claim 10 in which said trackmeans includes aligned facing surface members on said first and secondarms defining a passage between said surface members.
 12. The apparatusin claim 11 in which said ram member includes a first portion in saidpassage between said surface members and a second portion pivotallymounted to said pallet support cradle.
 13. The apparatus in claim 8 inwhich said pallet support cradle includes a sacrificial member adjacentsaid first and second circular blades when said cradle is in said secondposition, said sacrificial member selected to be substantiallynondamaging to said blades.
 14. The apparatus in claim 8 in which eachof said first and second blades is made from steel and has an innerportion adjacent its center and an outer portion adjacent its cuttingedge and wherein said outer portion is harder than said inner portion.15. The apparatus in claim 8 in which each of said first and secondblades includes means defining a center hole therein, said first andsecond blades being mounted to the associated one of said first andsecond arms by rotatable mounting means, said rotatable mounting meansincluding a spindle, a bearing having an outer race and an inner race,means for fastening said inner race to said spindle, means for fasteningsaid outer race to said blade, cover means for closing said center holeand means for fastening said cover means to said spindle.
 16. Theapparatus in claim 8 in which each said first and second connectingmeans includes a plate spanning the associated pair of said armsadjacent the associated said blades, said plate having a chamferedleading edge and a double-beveled trailing edge.
 17. An apparatus forunnailing wood pallets having first and second spaced sets of slatsnailed to opposite sides of a plurality of wood stringers, saidapparatus comprising:first arm assembly having first cutting means forcutting nails and horizontally elongated support means for supportingsaid first cutting means; second arm assembly having second cuttingmeans for cutting nails and horizontally elongated support means forsupporting said second cutting means; means movable with at least one ofsaid first and second support means for defining a track; a palletmoving means for moving a pallet between a first position away from saidarm assemblies and a second position subjacent said arm assemblies; astringer return means for moving a stringer from said second position tosaid first position, said stringer return means including a memberhaving surface means for abutting a stringer, follower means forfollowing said track and mounting means for mounting said member to saidpallet moving means such that said member horizontally moves with saidpallet moving means and said follower means is vertically adjustable.18. The apparatus in claim 17 in which said member is elongated andwherein said surface means is at one end of said elongated member,wherein said follower means is adjacent said surface means and furtherwherein said mounting means includes means for pivotally mounting asecond end of said elongated member opposite said one end to said palletmoving means.
 19. The apparatus in claim 18 in which said track includesfirst guide surface means along said first support means and secondguide surface means along said second support means and facing saidfirst guide surface means such that said first and second guide surfacemeans defining a space therebetween.
 20. The apparatus in claim 19 inwhich said follower means includes a widened portion of said memberconfigured to fit said space between said first and second surfacemeans.
 21. The apparatus in claim 20 in which said member is made from apolymer.